1. Field of the Invention
Embodiments of this invention relate to in situ shutoff gel compositions having controlled crosslinking properties and for methods for making and using the compositions.
More particularly, embodiments of this invention relate to in situ shutoff gel compositions having controlled crosslinking properties, where the compositions include a crosslinkable polymer system, a crosslinking system, a crosslink delay system and a solvent system. Embodiments of this invention also relate to methods for making and using the situ shut-off gel compositions.
2. Description of the Related Art
Certain formation include relatively high permeability zones and relatively low permeability zones and zone having moderate permeability. Poor areal conformance formations including high permeability streaks and high permeability anomalies within a formation matrix. Fluids introduced into such formations generally exhibit poor flow profiles and sweep efficiencies and have poor vertical or areal conformance.
A number of attempts to remedy such conformance problems exist. U.S. Pat. Nos. 3,762,476; 3,981,363; 4,018,286; and 4,039,029 to Gall or Gall et al describe various processes wherein gel compositions are formed in high permeability zones of subterranean formations to reduce the permeability therein. According to U.S. Pat. No. 3,762,476, a polymer such as polyacrylamide is injected into a formation followed sequentially by a crosslinking agent. The sequentially injected slugs are believed to permeate the treatment zone of the formation and gel in situ.
An attempt to achieve delayed polymer gelation was U.S. Pat. No. 4,706,754 to Smith which describes a process for reducing formation permeability by using polyacrylamide gels in combination with a crosslinking agent and a carboxylic acid delaying agent. The delaying agent allows for the gelation solution to thoroughly mix and be placed in the desired treatment region up to about 24 hours before gelation occurs. However, it is often desirable to delay gelation for longer than 24 hours to enable a gel to be placed at distances from the injection well that takes longer than 24 hours to achieve.
U.S. Pat. No. 4,744,418 to Sydansk discloses that at temperatures below 140° F. (60° C.), gelation can be delayed by decreasing the amount of polymer hydrolysis. U.S. Pat. No. 4,844,168 also to Sydansk discloses that above temperatures of about 140° F. (60° C.) polyacrylamide autohydrolysis increases at a rate that is proportional to the increase in temperatures. Sydansk also discloses that delayed gelation can be achieved at temperatures above about 140° F. (60° C.) by utilizing polyacrylamide having less than 0.1% hydrolysis. Sydansk is able to achieve delays in gelation of up to about 168 hours at about 165° F. (74° C.) and up to about 20 hours at temperatures of about 219° F. (104° C.). However it is often desirable to delay gelation for longer than 168 hours at temperatures of about 165° F. (74° C.) and longer than 20 hours at temperatures of about 219° F. (104° C.). Therefore a need exists for a gelation process wherein gelation delays can be enhanced when reservoir temperatures exceed 165° F. (74° C.) and exceed 219° F. (104° C.).
More recently, U.S. Pat. No. 5,069,281 disclosed using buffers having pKa values between 3.5 and 6.8 made of a mono-carboxylic acid or mono-carboxylic acid salt or mixtures to control the crosslinking process of chromium with polyacrylamides having less than 0.1% of hydrolysis. U.S. Pat. No. 5,421,411 disclosed using mono-carboxylic and/or poly-carboxylic acid and derivatives to delay the crosslinking process of polyacrylamides with a degree of hydrolysis higher than 0.1%.
Thus, there is a need in the art for gel systems and processes that are capable of forming gels having a predetermined gelation rate, strength, and stability to satisfy particular demands of a subterranean hydrocarbon-bearing formation.